Laser-Based 3D Printing Used to Fabricate Tiny Microstructures for Tissue Repair

The researchers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland are already well known for their work in robotics, microscopy, and spectroscopy, but now they’re researching a new and innovative approach to repairing tissue damage, using 3D printing technology, that could be used with an endoscope to build biocompatible microstructures right into tissue inside the body. Now, for the first time, an optical fiber that’s as thin as a human hair can use laser-based 3D printing to fabricate tiny structures.

Existing laser-based microfabrication techniques use two-photon photopolymerization – a non-linear optical phenomenon – to selectively cure a volume that’s deep inside a liquid photosensitive material. But, these are not the easiest methods when it comes to biomedical applications, because the process needs unwieldy optical systems and complex (read: expensive) lasers that emit very short pulses to deliver the light. So the researchers figured they could simplify the system setup.

“Our group has expertise in manipulating and shaping light through optical fibers, which led us to think that microstructures could be printed with a compact system. In addition, to make the system more affordable, we took advantage of a photopolymer with a nonlinear dose response. This can work with a simple continuous-wave laser, so expensive pulsed lasers were not required,” explained research team leader Paul Delrot from EPFL.

“With further development our technique could enable endoscopic microfabrication tools that would be valuable during surgery. These tools could be used to print micro- or nano-scale 3D structures that facilitate the adhesion and growth of cells to create engineered tissue that restores damaged tissues.”

The research team detailed their approach, which can 3D print microstructures with a 1.0-micron lateral (side-to-side) and 21.5-micron axial (depth) printing resolution, in a paper titled “Single-photon three-dimensional microfabrication through a multimode optical fiber” in the Optical Society of America (OSA) journal Optics Express; co-authors include Delrot, Damien Loterie, Demetri Psaltis, and Christophe Moser, all from EPFL’s School of Engineering.

The tiny microstructures were fabricated on a microscope slide, but the approach could also be used to study how cells interact with different microstructures in animal models, which would be one step closer to endoscopic 3D printing inside people.

Researchers dipped the end of a thin optical fiber into a photopolymer and cured it, using the fiber to digitally focus and deliver laser light point-by-point into the liquid to build 3D microstructures. Taking advantage of a chemical phenomenon where solidification happens above a certain light intensity threshold, the team selectively cured a set volume of material with an inexpensive, low-power laser that emits light continuously, instead of just short pulses.

An organic polymer precursor, doped with a photoinitiator made with off-the-shelf chemical components, was used to make both solid and hollow microstructures. The team focused a continuous-wave laser emitting light at a safe wavelength of 488 nanometers through an ultra-thin optical fiber – it was so small, it could fit inside a syringe. Then, after a calibration step allowed them to digitally focus and scan light through the fiber without moving it, the researchers used wavefront shaping to focus the laser light inside the photopolymer, so only a tiny 3D point was cured.

Delrot said, “Compared to two-photon photopolymerization state-of-the-art systems, our device has a coarser printing resolution, however, it is potentially sufficient to study cellular interactions and does not require bulky optical systems nor expensive pulsed lasers. Since our approach doesn’t require complex optical components, it could be adapted to use with current endoscopic systems.”

The research team is working toward clinical use for their technique, and is currently developing biocompatible photopolymers and a compact delivery system. The team is also thinking about a faster scanning speed, but a commercial endoscope could be used in place of an ultra-thin optical fiber if the size of the instrument is not important. They also need to develop a method for finishing and post-processing the 3D printed microstructure inside the body, for biomedical purposes.

“Our work shows that 3D microfabrication can be achieved with techniques other than focusing a high-power femtosecond pulsed laser. Using less complex lasers or light sources will make additive manufacturing more accessible and create new opportunities of applications such as the one we demonstrated,” said Delrot.

Since this new, compact microfabrication tool can 3D print delicate details onto larger parts, it could even be added to existing commercially available 3D printers.

Delrot said, “By using one printer head with a low resolution for the bulk parts and our device as a secondary printer head for the fine details, multi-resolution additive manufacturing could be achieved.”

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[Source: The Optical Society of America]